1. FIELD OF THE INVENTION
This invention relates to exhaust emission control devices of the catalyst type for internal combustion engines mounted on motor vehicles or the like, and more particularly it is concerned with an exhaust emission control device of the type described which comprises a novel catalyst element container and catalyst element holder combination.
2. DESCRIPTION OF THE PRIOR ART
In one type of devices known in the art for removing noxious components of exhausts vented to atmosphere from internal combustion engines mounted on motor vehicles or the like, such as carbon monoxide, unburned hydrocarbons and oxides of nitrogen, a catalyst has been used. Many exhaust emission control devices of the catalyst type employ a catalyst in particulate form. Proposals have been made to use, in place of the catalyst of the particulate form, a catalyst element comprising a catalyst composition carried by a carrier (the carrier is generally of a honeycomb structure in many cases) made of ceramic in one piece and formed therein with a plurality of exhaust passages.
The catalyst element of the honeycomb structure has, however, the disadvantage of being susceptible to forces of impact and vibration. In order to obviate this problem, it has been proposed to use a metallic woven fabric 3 of high stability which is mounted between a wall of a container 1 and the catalyst element 4 as shown in FIG. 1. It has also been proposed to fit a ring 2 over each of opposite ends of the catalyst element 4 and seal it by closing a gap between the wall of the container and the catalyst element in which metallic woven fabric 3 is mounted, in order to preclude leak of exhausts through the gap to an outlet port 1b after being introduced into the container through an inlet port 1a.
Some disadvantages are associated with the aforementioned devices of the prior art. There are differences in thermal expansivity between the container 1 or rings 2 and the catalyst element 4, so that a gap tends to be formed between each of the rings 2 and the catalyst element 4. Thus, exhausts not purified yet may leak through the gaps, pass through a gap in which the metallic woven fabric 3 is mounted and be discharged through the outlet port 1b. When the temperature in the container is elevated, the resilience of the metallic woven fabric 3 tends to be reduced, so that when the container 1 is subjected to forces of impact or vibration the catalyst element 4 may strike against the rings 2, thereby damaging the catalyst element.